I can only tell you what I do, so don't take it as being a definative answer. I have had a rust problem amd bit the bullet (or maybe its I took a bullet in $$$) based on the recommendations of a commercial operation in southheast North Carolina (since I spent a few hours with them a couple of years ago). I've since been told that the same fungicides work for leaf streak.
However, Mancozeb is not so terribly expensive and is a contact killer for the rust spores, so it should kill-on-contact for leaf streak fungus too. This was not among the original recommendations, however. Those were to alternate between two different strobulines (the ones that are made out of gold or something equally expensive), Compass and Strike. I was later told by a very knowledgeable lady in Canada that you should not atlernate between two of these chemicals because resistance can be acquired, and once it is acquired, it will block all strobulins. So this year's plan is to rotate three - Mancozeb, Strike, and Compass. For me (and a University of Gerogia study agreed!!) one of the two strobulins really does not control rust very well while the other is much better, so I might eliminate the poorer one. I just can't remember which one it is at the minute. Note that there are everal different types of strobulins, but the one in Heritage was the most effective in the UGA study. I've attached the link to their PowerPoint presentation. Go through it until you find their conclusions and recommendations. Their recommendation is to use one of the sort-of systemic ones that works and alternate that with Mancozeb. That should take care of the leaf streak and any runs that gets blow in by the wind. For rust, you have to continue this all season if you don't it to show up once the weather breaks - - for us that is mid-to-late September

I am assuming that since this works for rust, it will work for leaf streak funguds too.
Larry

Here is a link that might be useful: Pathway to UGA Rust Study

This link gives recommendations for leaf streak fungicides. Sweatin_in_ga, from what I remember Strike is not a strobilurin.

Here is a link that might be useful: Fungicides for Leaf Streak

Yes, Daniel, you are right. Strike is an organic ending with 'butanone.' I looked up the e-mail that I got and it said that both Compass (strobilurin) and Strike (butanone) were semi-systemic (no daylily rust fungicide product is truly systemic like certain insecticides are) and that I needed to add contact killer to my mix for daylily rust. Sorry about my error.
The site you recommend is good, but for those who cannot find the specific brand names, I looked up the active chemical group so they can look for the active ingredient of the best ones if they are available from any other manufacturer.

Cleary's 3336G - - thiophanate-methyl available to residential customers only as a powder
Cygnus 50 WDG - - kresoxim methyl
Systhane 40WP - - mycolbutanil
Terraguard 50 - - triflumizide
Headsup 100 - - saponins of Chenopodium quinoa
Daconil - - Chlorothalonil

Note: Headsup is an natural product isolated from quinoa, a grain cultivated for centuries in the Andes mountains.

Never heard of butanone, I thought Strike was triadimefon, same as in Bayleton. So I looked it up and butanone is part of the long unintelligible chemical name, but still triadimefon.

Daniel,
Can you recommend something for Danielle?

Nothing more than the link I posted above that said Cleary's and Systhane are the most consistently effective if I'm reading it right and also lists which fungicides didn't work at all. Wish I could help more.

Thanks Larry & Daniel for the responses and additional links. I've been busy the last week and forgot to check back on this thread but wanted to let you know I appreciate the info.

After posting my message I kept doing some more research on the internet and am even more confused now about what exactly is plaguing my daylilies. I mentioned that the aphids were particularly bad this year and I've only recently gotten around to combatting them even though they've been active for weeks and some plants are heavily infested. I always thought aphids were more of a minor nuisance but some websites are saying that severe aphid damage can actually resemble leaf streak or rust. I didn't realize just how heavy my infestation was until I took a much closer look the other day while cutting back some really diseased-looking plants and found loads of them hiding deeper down in the foliage than I had looked before. There is definitely a correlation because the more heavily aphid-infested plants all exhibit greater degrees of the leaf-streak like spots, streaks and browning. I'm not sure if the aphids were more drawn to already fungus-infected and weakened plants or if the reverse is true and the aphids attacking them is causing the unsightly appearance and opened the door for the fungus to take hold.

Before spending alot of money I've decided to try and eliminate the aphids, cut back the really damaged/infected leaves and give them some time to recover. If I still see new leaves emerging that become infected then I'll "bite the bullet" as Larry put it and invest in some of the expensive fungicides ya'll recommended. I'm definitely leaning toward Cleary's after reading that study but haven't made up my mind about what to alternate it with just yet. I also liked what I've read about Compass but I think its beyond my budget.

Danielle

I like your plan, Daniel. Start with clearing up the aphids. There have been a couple of posts regarding that recently. Options range from very "green" (hosing them down every day or two) to insecticidal soap, to contact sprays (Malthion which kills what it contacts but does not always get in between the leaves), to a strong systemic (like Acephate). Once the aphids are cleared up, then you can know for sure which came first, aphids or leaf streak. You can also use ladybugs or other beneficial inscets as a control, but some of the chemcials will kill them too, so make sure your plan gets you where you want to go efficiently. I've not lookled much, but Cleary's 3336 is available on-line for about $68 for a quart. Rosemania offers Eagle 20EW for about $60 per pint, but I could not find the chemcial concentration for Eagle 20EW, so it may be cheaper more concentrated) or more expensive (less concentrated) per unit of actual chemical.
Larry

Jim Murphy (registered plant pathologist) says the best is Cleary's 3336. You MUST apply it early in the season however. I was able to order the liquid online from somewhere in GA although I couldn't get it here in Va.